Definitions Flashcards Preview

Propositional Logic > Definitions > Flashcards

Flashcards in Definitions Deck (39)
Loading flashcards...

When are atomic propositions s and t logically equivalent?

Atomic propositions s and t are logically equivalent if the bicondtional s t is a tautology.


How does validity relate to tautology?

argument valid IFF conditional who’s antecedent is conjunction of all premises and consequent is conclusion is tautology i.e. (P1 ^ P2 ^ …) —> C


Outline the required rules of inference



What is ex falso quodlibet and what does it show?

Ex falso quodlibet (principle of explosion): p, -p, therefore q. It is valid!!! No rows in truth table where both premises T but C is F. This shows that as soon as there is a contradiction in your belief system, then you should believe everything.


State De Morgan's laws

¬(p ^ q) is logically equivalent to ¬p v ¬q i.e. the negation of a conjunction is the disjunction of the negations.

¬(r v s) is logically equivalent to ¬r ^ ¬s i.e. the negation of a disjunction is the conjunction of the negations.


Outline 6 steps to critically engage with an argument

paraphrase the argument

diagram the argument

make an ‘implicit’ critique - point out implicit propositions

make a formal critique i.e. formal fallacies

make an informal critique i.e. informal fallacies

is it sound? demonstrate that you understand what it is for each premise to be false


What is the biconditional of p & q equivalent to?

(p ^ q) v (-p ^ -q) or (p --> q) ^ (q--> p)


What is a ^ -b equivalent to?



How do we challenge hypotheticals?

we challenge it by imagining a situation where the antecedent holds, but the consequent fails.